[Beowulf] To the bandwidth junkies

Håkon Bugge hbugge at platform.com
Thu Jan 29 19:10:18 EST 2009


I just ran stream_omp (C code) and noticed the average timing often  
was less than minimum timing.
Turns out, there is a bug in the code (snip from http://www.cs.virginia.edu/stream/FTP/Code/Versions/stream_omp.c) 
:

     for (k=1; k<NTIMES; k++) /* note -- skip first iteration */
	{
	for (j=0; j<4; j++)
	    {
	    avgtime[j] = avgtime[j] + times[j][k];

and later:

     for (j=0; j<4; j++) {
	avgtime[j] = avgtime[j]/(double)NTIMES;

Obviously, the divisor should have been (NTIMES-1).


As a curiosity, the first time I corrected a well known and publicly  
used benchmark was in 1986, http://mvb.saic.com/freeware/vax88a3/rcas88/nets88/gnucbench.txt

Am I getting too old for this?



Thanks, Håkon


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